The answer to this question may seem obvious to Haaretz readers and to the impressive roster of world leaders gathering at Yad Vashem this week for the Fifth World Holocaust Forum, marking 75 years since the liberation of Auschwitz.

Holocaust denial is a vile assault on the memory of the six million Jews murdered by Nazi Germany and its accomplices, a depraved twisting of the anti-Semitic knife. We must be unstinting in our efforts to keep the memory of our lost relatives - and the historical record - alive.

But beyond that, the question of what Holocaust denial really means, and where the boundaries of denial start and stop, is not so clear. In a world where social media platforms are willing facilitators of the notion that historical truth is just not that important, propagandists and conspiracy theorists from across the political spectrum latch on to the Holocaust to make political capital for themselves.

How social media has helped Holocaust denial morph from a neo-Nazi lie to an a ubiquitous, and accepted,internet meme becomes clear when contrasting how the European Court of Human Rights has approached Holocaust denial, and how social media titan Facebook has.

The Court is part of an extensive framework of institutions and conventions carefully constructed by the nations of post-Holocaust Europe to try to prevent the return of the totalitarianism that brought about a genocide on their soil.

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In a significant ruling last October, the Court found that Holocaust-denying German politician Udo Pastrs, the former Chair of the far right NPD, had lost his protected right to free speech when he "intentionally stated untruths in order to defame the Jews and the persecution that they had suffered" by contradicting "established historical facts" in relation to the Holocaust.

This ruling upheld the values of the post-war West European order that Holocaust denial was originally intended to subvert.

Denial began as a far right project to rehabilitate Nazism by erasing its greatest crime from the worlds collective memory. Persuade people that the Holocaust never happened, so their thinking went, and Nazism and fascism become just another ideology: brutal and uncompromising, perhaps, but no more so than communism and its variants. This approach had the added anti-Semitic bonus of arguing that the entire world and Germans and Palestinians specifically were the victims of a gigantic Jewish hoax.

The heyday of this movement was the 1980s and 1990s, when its leading figures were authors and academics like David Irving and Robert Faurisson. Irving was, for a while, one of Britains best-known historians of World War Two; Faurisson was a university professor who was defended by Noam Chomsky when his denial writings came to light.

With a surge in far-right activity and support across Europe following the fall of the Berlin Wall, there was genuine fear that Holocaust denial might build into a significant force. But today, Irving is discredited, Faurisson is dead, and the latest generation of neo-Nazi Jew-haters prefer to celebrate the Holocaust than to deny it.

Instead, the new promoters of Holocaust denial are the social media platforms and tech companies that have done more than any far right propagandist to undermine the notion of historical truth and to challenge the assumptions of liberal democracy.

Denial has found a new home as one amongst many conspiracy theories; another opportunity for online hucksters in YouTube videos and Facebook groups to persuade the gullible and the ignorant. As such it has greater appeal across the political spectrum than it ever did, reaching people who would never think of themselves as neo-Nazis or anti-Semites.

Facebook persistently contendsthat it will not remove Holocaust denial posts from its platform unless deniers also incite hate or violence against Jews. According to Facebook CEO Mark Zuckerberg, Holocaust denial is just people "getting it wrong." The idea that Holocaust denial, by definition, incites hate against Jews holds no sway with the worlds largest social network.

Social media is, of course, a global network, and awareness of even the basic facts of the Holocaust varies alarmingly from country to country. A CNN poll in 2018 found that a fifth of French adults under the age of 34 had never heard of the Holocaust, compared to just five per cent in Germany. Another 2018 poll found that 31 per cent of adults in the United States thought two million Jews or fewer were killed.

Outside of Europe and the Americas knowledge of the Holocaust drops even further. According to an Anti-Defamation League poll of 102 countries in 2014, most people in the Middle East, north and sub-Saharan Africa and in Asia had not heard of the Holocaust, and of those who had, substantial proportions in each country thought it was either exaggerated or a complete myth.

This is fertile soil for todays revisionists, relativisers and minimizers of the Holocaust. The claim that Israel behaves just like Nazi Germany and that Palestinians, rather than Jews, are Nazisms most enduring victims, is ubiquitous on the anti-Israel left. It is mirrored on the right by the idea that, just as Jews suffered under Nazism, so Poles, Hungarians, Lithuanians, Ukrainians and others suffered under communism; combined with a determined effort to erase examples of local collaboration in the extermination of their Jewish populations from these countries own national narratives.

Neither of these approaches - emerging from the anti-Israel left and the hard nationalist right - denies that the Holocaust happened and both recognize it as a terrible crime. Rather than denial, they have developed their own mythology to harness the Holocausts unrivalled moral weight for their own political projects.

If you believe that the Jews exploit the Holocaust for their own particular ends, it makes sense to try to do the same for yourself. And if you see Holocaust commemoration as a vehicle for Jewish power and privilege, what betterway to undercut that "power" is there than an interpretation of the Holocaust thatreframes it asyour own victimhood story, while transferring some of the blame onto the Jews themselves?

This leads to the grotesque situation of the former Mayor of London Ken Livingstone insisting that Hitler was "supporting Zionism" in the 1930s because it fits his leftist anti-Zionism, to bolster his characterization of Israel as morally illegitimate; while George Soros, who survived the Holocaust as a child, is accused by his right-wing critics of having actually collaborated with the Nazis.

Both claims are nonsense: but in this post-truth, identity-driven politics, where people choose their own facts and ignorance is no barrier to the assertion of expertise, why risk a formal charge of "Holocaust denier" when you can twist six million victims into whatever shape you want, and then adopt that "Holocaust" as your own.

Dr Dave Rich is Director of Policy for the Community Security Trust, an Associate Research Fellow at the Pears Institute for the Study of Antisemitism, Birkbeck, University of London, and author of The Left's Jewish Problem: Jeremy Corbyn, Israel and Antisemitism (Birkbeck, 2018). Twitter: @daverich1